Question

Review of the woman, the barbell, and the Earth (Section 7.9 in the textbook). Starting from rest, a woman lifts a barbell with a constant force F through a distance h, at which point she is still lifting, and the barbell has acquired a speed v. Let Ewoman stand for the following energy terms associated with the woman:

Ewoman = Echemical,woman + Kwoman (moving arms etc.) + Ugrav,woman+Earth + Ethermal,woman
The change in the kinetic energy of the barbell is (1/2)mv2 - 0 = (1/2)mv2.
The general statement of the energy principle is deltacapEsys = Wext. We'll consider terms on the left side of the equation (the deltacapEsys side, changes in the energy inside the system) and terms on the right side (the Wext side, energy inputs from the surroundings).
I. System: Woman + barbell + Earth For the system consisting of the woman, the barbell, and the Earth, which of the following terms belong on the left side of the energy equation (the deltaEsys side)?
deltaEwoman
-mgh
-Fh
Fh
-(1/2)mv2
+mgh
none of these terms (left side is 0)
(1/2)mv2
For the system consisting of the woman, the barbell, and the Earth, which of the following terms belong on the right side of the energy equation (the Wext side)?
Fh
-mgh
+mgh
-(1/2)mv2
deltaEwoman
-Fh none of these terms (right side is 0)
(1/2)mv2
II. System: barbell only For the system consisting of the barbell only, which of the following terms belong on the left side of the energy equation (the deltacapEsys side)?
eltacapEwoman
-mgh
+mgh
-(1/2)mv2
Fh (1/2)mv2 n
one of these terms (left side is 0)
-Fh
For the system consisting of the barbell only, which of the following terms belong on the right side of the energy equation (the Wext side)?
-Fh
-mgh
+mgh
(1/2)mv2
-(1/2)mv2
Fh
none of these terms (right side is 0)
ΔEwoman
III. System: barbell + Earth For the system consisting of the barbell and the Earth, which of the following terms belong on the left side of the energy equation (the Esys side)?
-Fh
-(1/2)mv2
Fh
(1/2)mv2
none of these terms (left side is 0)
ΔEwoman
+mgh
-mgh
For the system consisting of the barbell and the Earth, which of the following terms belong on the right side of the energy equation (the Wext side)?
1/2)mv2
ΔEwoman
+mgh
-(1/2)mv2
none of these terms (right side is 0)
Fh
-mgh
-Fh

Answer 1

I. System: Woman + Barbell + Earth

Left side:
`\(\Delta E_{\text{woman}}\)`

Right side:
`\(Fh\)`

II. System: Barbell only

Left side: None of these terms (0)

Right side:
`\(Fh\)`

III. System: Barbell + Earth

Left side: None of these terms (0)

Right side:
`\(-Fh\)`

I. System: Woman + Barbell + Earth

Left side of the energy equation (deltaEsys side):

`\(\Delta E_{\text{woman}}\)`

(This includes all the energy terms associated with the woman: chemical energy, kinetic energy due to movement, gravitational potential energy, and thermal energy.)

Right side of the energy equation (Wext side):

`\(Fh\)`

(This is the work done by the woman in lifting the barbell through a distance
`\(h\)`.)

II. System: Barbell only

Left side of the energy equation (deltaEsys side):

None of these terms (Since the system is only the barbell, there is no change in the woman's energy, so
`\(\Delta E_{\text{woman}} = 0`).

Right side of the energy equation (Wext side):

`\(Fh`

(This is the work done by the woman in lifting the barbell through a distance
`\(h\)`.)

III. System: Barbell + Earth

Left side of the energy equation (deltaEsys side):

None of these terms (The system is the barbell and the Earth, and there is no change in the woman's energy, so
`\(\Delta E_{\text{woman}} = 0`).

Right side of the energy equation (Wext side):

`\(-Fh\`

(This is the work done by the gravitational force as the barbell is lifted against gravity.)

Summary:

I. System: Woman + Barbell + Earth

Left side:
`\(\Delta E_{\text{woman}}\)`

Right side:
`\(Fh\)`

II. System: Barbell only

Left side: None of these terms (0)

Right side:
`\(Fh\)`

III. System: Barbell + Earth

Left side: None of these terms (0)

Right side:
`\(-Fh\)`

It's important to note that the energy principle states that the change in the total mechanical energy of the system is equal to the work done on the system by external forces. In this case, the external force is the force applied by the woman in lifting the barbell against gravity. The calculations involve understanding the contributions of different energy terms and their changes in each system.